Solute Transport in the Bone Lacunar-Canalicular System

描述（由申请人提供）：骨细胞是骨中数量最多的细胞，对骨健康和骨质量至关重要。它们对骨骼感知和适应机械刺激以及重塑受损组织至关重要。由于骨细胞完全包裹在矿化骨基质中，它们的存活和功能完全依赖于溶质（代谢物、生长因子、细胞因子和其他信号分子）通过腔隙-管状系统（LCS）的运输。尽管在描述骨中的运输途径方面取得了进展，但对于生物分子在体内进出骨细胞的机制知之甚少。这反映了缺乏在活体动物的实时条件下研究这些问题的方法。为此，我们最近开发了一种基于光漂白后荧光恢复（FRAP）的新成像方法，可以原位实时测量骨LCS中的溶质运动（Wang等，2005）。科学通报，2002(2):1 - 11。我们建议将这种新方法与数学/计算建模相结合，以充分表征骨中的扩散和对流。为了验证由机械载荷引起的对流是LCS中大分子移动的主要机制这一假设，我们将首先量化死后骨骼中不同大小溶质的基线扩散运输。随后将在活体动物中测量由血压和机械负荷驱动的对流输送。这些研究将描述对骨细胞活力和骨机械转导至关重要的转运机制，并为其他生物和工程系统（如组织工程支架）的质量转运提供新的见解。分子如何在骨内运动的详细知识将有助于确定分子参数，如流体动力学半径和新药的半衰期，以便将它们有效地输送到骨中以治疗骨质疏松症和关节炎等疾病。我们的具体目标是：1)确定溶质在骨LCS中的扩散如何取决于溶质的分子量；2)确定血管压力对骨LCS内溶质转运的影响；3)确定机械载荷对骨LCS中溶质运输的影响。

DESCRIPTION (provided by applicant): Osteocytes, the most numerous cells in bone, are critical for bone health and bone quality. They are essential for bone to sense and adapt to mechanical stimuli and to remodel damaged tissue. Since osteocytes are completely encased in mineralized bone matrix, their survival and function are entirely dependent on transport of solutes (metabolites, growth factors, cytokines, and other signaling molecules) through the lacunar-canalicular system (LCS). Despite advances in delineating transport pathways in bone, little is known about the mechanisms involved in moving biological molecules to and from osteocytes in vivo. This reflects a lack of methods available to study these questions under real-time conditions in living animals. To this end, we recently developed a new imaging method based on Fluorescence Recovery After Photobleaching (FRAP) that allows measurement of solute movement in the bone LCS in situ and in real-time (Wang et al.,2005. Proc Natl Acad Sci 102:11911). We propose to use this novel approach in combination with mathematical / computational modeling to fully characterize diffusion and convection in bone. To test the hypothesis that convection due to mechanical loading is the primary mechanism for moving large molecules in the LCS, we will first quantify the baseline diffusive transport of solutes of various sizes in post-mortem bones. Convective transport driven by blood pressure and mechanical loading will be subsequently measured in live animals. These studies will delineate the transport mechanisms that are essential for osteocyte viability and bone mechano-transduction, and provide new insights into mass transport in other biological and engineered systems (e.g., tissue engineering scaffolds). Detailed knowledge of how molecules move within bone will help define molecular parameters such as hydrodynamic radii and half-life times for new drugs so that they can be delivered effectively into bone to treat diseases such as osteoporosis and arthritis. Our specific aims are: 1) to determine how solute diffusion in the bone LCS depends on the solute's molecular weight; 2) to determine how solute transport in the bone LCS is affected by vascular pressure; 3) to determine how solute transport in the bone LCS is affected by mechanical loading.